30results about How to "Avoid Harmonic Pollution" patented technology

The invention belongs to the technical field of frequency converters and provides a four-quadrant frequency converter. According to the four-quadrant frequency converter, a frequency converter is arranged between a power grid and an induction motor; an energy feedback unit is arranged at a direct current (DC) busbar side of the frequency converter; a negative pole end DC- of a direct current busbar on the frequency converter is electrically connected with the DC- of the energy feedback unit; the DC+ on the frequency converter is electrically connected with DC+ of the energy feedback unit; three-phase alternating current output of the energy feedback unit is connected to input sides R, S and T of the frequency converter in parallel; a PE (Protecting Earthing) terminal of the energy feedback unit is reliably connected to the ground; when the busbar voltage of the frequency converter is detected by the energy feedback unit to be up to a set valve, feedback electric energy is converted to power frequency and transferred to the power grid to carry out energy saving regulation. The four-quadrant frequency converter provided by the invention has the advantages that through an external energy feedback device, the electric energy produced by the motor is added to the input end to the frequency converter after feedback and an electric reactor is additionally arranged to avoid the harmonic pollution, so that the power factor is greatly improved and the efficient utilization ratio of the electric energy is realized.

The invention relates to a micro power consumption elevator, which comprises a motor, a frequency converter and an encoder. The micro power consumption elevator is characterized by further comprising a super-capacitor component, wherein an positive electrode of the super-capacitor component is connected with a positive electrode input end of the frequency converter; an negative electrode of the super-capacitor component is connected with a positive electrode input end of the frequency converter; in a motor power generation state, the super-capacitor component stores the electric energy generated by the motor, and in a motor electro-motion state, the super-capacitor component supplies power to the motor for running; and an energy supplement device charges the super-capacitor component when the working voltage of the super-capacitor component is lower than a designed voltage lower limit value. The micro power consumption elevator has the advantages that the super-capacitor component is used as a main power supply carrier for continuously supplying power to the elevator and the super-capacitor component not only serves as an energy storage element but also serves as a battery and makes full use of the electric energy generated in the running process of the elevator so that a brake unit (or a brake resistor) is unnecessary to be arranged in the elevator, an inverter is also unnecessary to be arranged in the elevator, not only the equipment cost is saved, but also thermal pollutions and harmonic noise pollutions are avoided, and the micro power consumption elevator is more energy-saving and environment-friendly.

The invention belongs to the technical field of a wind power generator, and specifically relates to an off-course gear and off-course motor protection apparatus and method, and applicable to an off-course system of the wind power generator. A soft starter is connected between four sets of off-course motors and a power supply in series; the soft starter adopts a three-phase anti-parallel thyristor as a voltage regulator; and when the motor is started, the output voltage of the thyristor is increased gradually, and the motor is accelerated gradually until the thyristor is fully switched on, and the motor works on mechanical characteristic of a rated voltage. By virtue of the off-course driving system protection apparatus and method, the problems of increasing of maintenance cost of a wind generator set and influence to the use efficiency of a fan caused by abrasion, teeth collision and the like of an acceleration off-course speed reducer and an off-course bearing gear when static mechanical equipment is suddenly loaded with high moment can be solved; and therefore, smooth starting is realized, the starting current is lowered, and tripping caused by start overcurrent can be avoided.

The invention relates to a rail traction power supply system based on a flywheel energy storage device and a method for increasing power quality thereof. The system comprises a railway switching room, a flywheel energy storage device, a converter and step-down transformers respectively arranged on a phase a and a phase b of a power supply arm, wherein a fuse and a circuit breaker are arranged on the high-pressure side of each step-down transformer; in the whole electric circuit, the flywheel energy storage device is connected with feeding busbars a and b through the converter and the step-down transformers; the step-down transformers and a converter system are used for converting the single-phase alternating current on the feeding busbars into direct current and outputting to the flywheel energy storage device; the flywheel energy storage device is used for executing a control strategy in the manner of collecting the voltage and current of the converter system. According to the invention, complete three-phase voltage balancing and active power regulation can be realized; recycling and reutilization for the regenerative brake energy of the train are realized; the investment of the passing neutral section device is reduced; the running of the power system is more stable and the power quality of the system is increased; the rail traction power supply system is applicable to the common power grid and micro-grid.

The invention provides a starting device, a starting method and a power supply system for improving the starting current in a circuit. The starting device is connected in series with a heating element and consists of a starting impedor and a starting switch which are connected in parallel. When the heating element is started, the starting switch is turned off so as to turn on the starting impedor to divide the voltage and limit the current of the path; and after the heating element is fully started, the starting switch is turned off to make the two ends of the starting impedor have a short circuit, so that the heating element can work at a rated working current. The method for improving the starting current in the circuit comprises the following steps: connecting the starting device in series with the heating element; starting the heating element and turning off the starting switch at the same time; and after the heating element is fully started, turning off the starting switch. The power supply system comprises the starting device and / or the starting method. The starting device, the starting method and the power supply system have the advantages of effectively reducing the starting current, along with simple structure, no harmonic pollution and the like.

The invention discloses an intelligent mixed type high-pressure dynamic reactive compensation device which comprises a compensation cabinet, a temperature controller and a heat dissipation fan. The temperature controller is used for controlling temperature inside the compensation cabinet. The compensation cabinet comprises a filter, a group of capacitors which are connected in parallel and a group of electric reactors which are connected in parallel. The electric reactors are adjustable electric reactors based on magnetic flux. A controller and a compensation control unit are further arranged inside the compensation cabinet. The controller is used for collecting three-phase high-voltage electricity. The compensation control unit comprises a trigger plate, a thyristor module and an insulated gate bipolar translator (IGBT) module. The compensation control unit receives a switching order of the controller, and is used for detecting of system parameters and compensation controlling of putting in and drawing out. The trigger plate adjusts the electric reactors in a double mode through the thyristor module and the IGBT module, a continuous stepless adjustable control mode is achieved, and adjusting range is wide.

The invention provides a direct-current auxiliary power supply system. The direct-current auxiliary power supply system comprises a high-voltage direct-current bus, a medium-voltage direct-current bus, a low-voltage direct-current bus, a direct-current auxiliary converter and a direct-current charger, wherein the high-voltage direct-current bus, the medium-voltage direct-current bus and the low-voltage direct-current bus are arranged on a rail vehicle; the direct-current auxiliary converter is connected between the high-voltage direct-current bus and the medium-voltage direct-current bus; thedirect-current charger is connected between the medium-voltage direct-current bus and the low-voltage direct-current bus; the high-voltage direct-current bus is connected to a contact net or a third rail and is used for supplying power to a traction motor of the rail vehicle; the direct-current auxiliary converter is used for supplying power to the medium-voltage direct-current bus; the medium-voltage direct-current bus is used for supplying power to each medium-voltage load in the rail vehicle; the direct-current charger is used for supplying power to the low-voltage direct-current bus; eachmedium-voltage load comprises a frequency-variable air conditioner; and the low-voltage direct-current bus is used for supplying power to a 110V-level storage battery of the rail vehicle. The direct-current auxiliary power supply system provided by the invention can effectively reduce the procedures of conversion of electric energy, can reduce electric energy loss, can improve the running efficiency of an auxiliary system, can lower the running cost of the overall auxiliary system and can improve the energy saving effect of the auxiliary system.

The invention discloses an alternating current servo loading test system, which comprises a servo twin trawling platform, a loading alternating current servo, a tested alternating current servo and aloading control platform, the servo twin trawling platform is used for fixing a tested alternating current servo and the loading alternating current servo; the tested alternating current servo is coaxially connected with the loading alternating current servo; the loading alternating current servo is connected to the power supply input end of the tested alternating current servo by leading out a direct current bus of the loading alternating current servo; and the loading control platform is used for controlling the tested alternating current servo and the loading alternating current servo. According to the invention, an energy feedback unit commonly used in the prior art is removed.The direct current bus loaded with the alternating current servo is led out and directly connected to the input end of the alternating current power supply of the tested alternating current servo, so that harmonic pollution caused by connection with an external network through the energy feedback unit is successfully avoided, the energy loss is reduced, and the installation cost of the test system is effectively reduced while the energy feedback efficiency is improved.

The present invention discloses a ship hybrid power propulsion system based on an active front-end frequency conversion technology. The system comprises a speed change generating set, an energy storage device, a transformer, a direct current distribution board, a propulsion motor, a constant voltage and constant frequency inversion module and an energy management system device. The speed change generating set is connected with a first active front-end rectifying device; a voltage regulation module and a second active front-end rectifying device are connected between the energy storage device and the transformer; the propulsion motor is connected with a motor inversion module; and air breakers are employed to connect the energy storage device with the voltage regulation module, to connect the first active front-end rectifying device with the energy storage device, to connect the first active front-end rectifying device with the direct current distribution board and to connect the secondactive front-end rectifying device with the direct current distribution board. The ship hybrid power propulsion system solves harmonic pollution, improves power supply conversion efficiency, improvesthe load rate of the generating set and achieves purposes of energy saving and emission reduction, reduction of cost and improvement of ship safety.

Provided total reactive power Q requested by system is supplied by n pieces of reactive compensation branch. A fixed capacitor is connected to a variable voltage source in one piece of compensation branch to supply 0-Q / n continuous controlled reactive power. Other n-1 pieces of compensation branch connect fixed capacitor to power source to supply fixed reactive powers. System reactive power is continuous controlled from 0-Q by continuous controlling reactive power in first piece of compensation branch and switching to other compensation branches. The capacity Qv of variable voltage source is only 1 / 4n of Q. Switching operation is implemented at time of zero current of all capacitors in n pieces of reactive compensation branch in order to avoid impulsion from electric network. Features are: low cost to realize reactive continuous control for electric network in high voltage, and prolonging service life of capacitor and switches.

The invention discloses a fast charging device for a storage battery system so that an alternating-current power supply and a storage battery pack are connected by the fast charging device and thus the rapid charging of the battery pack can be realized. An active filter, an alternating-current contactor and a three-phase rectifier bridge are connected based on phases successively; an input inductor and the input capacitor are connected in series and then are connected to positive and negative terminals of the output terminal of the three-phase rectifier bridge; the input terminal of an alternating-current conversion module is connected to the two ends of the input capacitor; and the output terminal of the alternating-current conversion module is connected to the input terminal of an isolation transformer. A high voltage direct-current relay, an output capacitor and a battery pack are connected in series; one end of the output capacitor is connected to the cathode of a diode rectifier bridge through an output inductor and the other end is connected with the anode of the diode rectifier bridge; and the output terminal of the diode rectifier bridge is connected to the output terminalof the isolation transformer. Therefore, charging efficiency of the battery is improved and the safety of the storage battery during the charging and discharging processes is enhanced.

The invention discloses a three-phase alternating current-to-N-phase alternating current direct type alternating current-to-alternating current converter based on cascade connection of single-phase transformers. The direct type alternating current-to-alternating current converter comprises three single-phase transformer commutation units and N LC filters. The cascaded direct-type AC / AC chopper in the single-phase transformer converter unit comprises one or more direct-type AC / AC choppers. According to the invention, the three-phase AC input voltage can be converted into the N-phase AC output voltage, and the frequency, amplitude and phase of the output voltage are independently controllable. The input sides of the cascaded direct AC / AC converters are coupled through the magnetic circuit of the transformer, so that current harmonic elimination can be realized, and harmonic pollution to input current caused by introduction of the current harmonic into the primary side of the transformer is avoided. In addition, bidirectional flow of energy can be realized, and a three-phase system and an N-phase system can be interconnected.

The invention provides a multi-pole coordinated energy saving device of a distributed type power distribution network. The coordinated energy saving device comprises a data acquisition device, a data integration device and a data monitoring device, which are connected in sequence; the problem of reactive power loss, caused by the fact that reactive power compensation of the power distribution network is not enough, is effectively solved; smooth compensation can be realized by adopting flexible and dynamic reactive power adjusting equipment; the compensation efficiency is high and the compensation degree is accurate; the power grid loss is reduced to the greatest extent; a reactive power compensation device is more stable in a reactive power compensation process and the service life of the reactive power compensation device is prolonged; harmonic pollution in the power distribution network can be effectively solved and normal and reliable operation of a power grid is guaranteed; an automation level of the power distribution network is improved; various devices automatically work and manual intervention can be reduced in an operation process of the power distribution network and the labor intensity of technicians is alleviated; furthermore, various parameters in a power grid operation process can also be collected by the coordinated energy saving device, and overhauling work of the technicians is facilitated.

The invention relates to a hybrid energy four-phase power transmission system. The hybrid energy four-phase power transmission system comprises a first energy circuit, a second energy circuit and a power grid three-phase power transmission line, the first energy circuit comprises a first power supply assembly, a first inlet wire, a first total outlet wire and a second total mixed outlet wire; the second energy circuit comprises a second A power supply assembly, a second A inlet wire, a second A outlet wire, a second B power supply assembly, a second B inlet wire and a second B outlet wire; a plurality of diodes are also included. The hybrid energy four-phase power transmission system has the advantages that clean energy is directly connected into the power grid, and the hybrid energy four-phase power transmission system is low in cost, small in loss, large in application range, convenient and simple.

The invention relates to a high voltage power supply, in particular to an adjustable high voltage power supply for a routine test station of a main converter cabinet of a locomotive, and solves the problems of high cost, unbalanced three-phase current and three-phase voltage of a power grid caused by single-phase power consumption and high probability of causing harmonic pollution to the power grid by a converter load and the like in a traditional high voltage power supply for the routine test station of the main converter cabinet of the locomotive. The adjustable high voltage power supply comprises a three-to-single-phase special transformer and two non-contact induction voltage regulators which are dragged by the three-to-single-phase special transformer, wherein the primary side of the three-to-single-phase special transformer is provided with two windings and the secondary side of the three-to-single-phase special transformer is provided with four windings; two windings on the secondary side are induced to one winding on the primary side respectively; the two windings on the primary side are connected end to end; and the four windings on the secondary side are connected in series, two windings on the secondary side are led in from the head end and led out from the tail end during the serial connection and the other two windings on the secondary side are led in from the tail end and led out from the head end. The high voltage power supply of the invention is particularly suitable for the routine test station of the main converter cabinet of the HXD2 type locomotive.

The invention provides a charging circuit and a control method thereof. The charging circuit only comprises a group of BUCK charging circuit, the number of the devices is small, and the cost of the devices is relatively low. The voltage input of a single bus is still used, and the states of a first selection unit S1 and a first selection unit S2 are controlled by the input according to whether the voltage of the commercial power is in the positive half cycle or the negative half cycle at present, so that whether a positive bus or a negative bus is accessed is determined, the BUCK step-down ratio is low, the stress of a first switch device Q1 is small, the efficiency is high, the electrolysis capacity of the bus does not need to be large, and the cost of the device is lowered. The technical scheme solves the problems in the prior art that the imbalance of positive and negative buses is caused by load dissymmetry of positive and negative buses and input imbalance of PFC positive and negative semi-cycle power is caused, so that the harmonic pollution caused to the power grid is avoided.

A distributed generation (DG) system and a micro power grid have great advantages in utilization of clean energy yet also face numerous problems. Detection of an island effect represents the key link in control over the DG system. The island effect refers to a situation when, due to such factors as a fault in the DG system or maintenance and the like, a large power grid is cut off or stops working, grid-connected equipment does not effectively detect a power failure state and disconnect DG equipment from the large power grid but still supplies energy to a local load. A conventional island detection technology can be divided into a passive detection method, an active detection method and a remote detection method. Compared to the prior art, the method provided by the invention has the following advantages: an island event is rapidly, accurately and reliably detected, the defect of a blind area existing by use of the passive method is effectively avoided, at the same time, injection of certain disturbance signals in a power network is unnecessary, the quality of output electric energy of the generation system is improved, and harmonic wave pollution is prevented.

The invention relates to a single-phase to three-phase power supply conversion system based on a power electronic transformer and a control method. The single-phase to three-phase power supply conversion system comprises a single-phase rectification input stage, a high-frequency transformation isolation stage, a three-phase inversion output stage and a low-pass filter, an uncontrolled rectification strategy is adopted for a transformer secondary side diode rectification circuit in the single-phase rectification input stage and the high-frequency transformation isolation stage; an EPWM controlstrategy is adopted to output high-frequency square waves for a transformer primary side single-phase inversion H-bridge circuit in the high-frequency voltage transformation isolation stage; and an SVPWM control strategy is adopted for the three-phase inverter output stage, and frequency conversion and voltage transformation control over the three-phase inverter output voltage is achieved. By adopting the conversion system and the control method system, the problems of distortion and harmonic pollution of three-phase alternating-current voltage waveforms after inversion can be avoided; and thedirect-current bus can obtain different levels of voltages through voltage transformation of the high-frequency transformer, so that voltage transformation and frequency conversion output after three-phase inversion is realized, and the three-phase inverter is used for an electricity utilization occasion of converting single-phase into three-phase power.

The invention discloses a photo-electrically isolated voltage buffer power supply. The photo-electrically isolated voltage buffer power supply is characterized by mainly comprising a control chip U2,a transformer T1, a transformer T2, a diode rectifier U1, an amplifier P, a triode VT1, a triode VT2, a triode VT3, a capacitor C3 and the like, wherein the positive electrode of the capacitor C3 is connected with the negative electrode output end of the diode rectifier U1 while the negative electrode of the capacitor C3 is connected with the positive electrode output end of the diode rectifier U1. The photo-electrically isolated voltage buffer power supply has relatively high bandwidth, so that the dynamic response speed of the power supply can be improved, thereby enabling an electrostatic dust collector to be higher in starting speed.

The invention discloses an EMI filter. The EMI filter is composed of an input capacitor, a transistor and a control circuit. The control signal generated by the control circuit dynamically changes the voltage at the first terminal of the transistor to compensate the voltage on the input capacitor of the switching power supply. Ripple, to get a smooth input current without switching frequency ripple. In order to prevent high-frequency harmonics from flowing into the power grid, causing harmonic pollution, and the technical implementation method of the present invention is simple, using semiconductor devices to filter out switching frequency ripples, which greatly saves space compared with passive devices, and is more suitable for full surface mounting device applications.

The invention discloses an LED drive circuit with output current self-adjustment capability, which comprises a single-phase AC input power supply, a rectifier bridge, a first power switch tube, a second power switch tube, a first power diode, a second power diode, a second power switch tube, and a second power switch tube. An inductor, a first capacitor, a second capacitor, a high-frequency transformer, a first current sampling resistor, a second current sampling resistor, a first voltage sampling resistor, a second voltage sampling resistor, a third voltage sampling resistor, and a fourth voltage sampling resistor , snubber resistor, snubber capacitor, snubber diode, active power factor correction module. The invention proposes a solution to solve the problem that LEDs work in the state of over-rated current for a long time due to the disconnection of parallel branch circuits. With the characteristics of high stability and safety, it is suitable for the control of various LED lighting circuits.

The invention provides a regional charging station control device with new energy power generation. The control device comprises a parameter collecting and processing unit for collecting and calculating voltage and current signal on the output side of the regional transformer when used and correspondingly emitting signals, a harmonic compensation unit for performing current compensation on a regional power grid corresponding to the received detection signal sent by a parameter acquisition unit, a charging station countercurrent control unit that controls whether the new energy generating device transmits power to the regional power grid according to a control signal sent by the parameter acquisition unit, and a charging power control unit correspondingly controlling the charging power of acharging station according to the control signal sent by the parameter acquisition unit. The device can effectively solve the harmonic pollution of the regional power grid by the regional charging station with new energy power generation, the reverse power supply of the new energy power generation device to the regional power grid, and the extreme situation that the regional transformer overloadcauses tripping outage which endangers regional power supply.

The invention discloses a voltage buffer power supply based on harmonic isolation. The characteristics lie in that the voltage buffer power supply is mainly composed of a control chip U2, a transformer T1, a transformer T2, a diode rectifier U1, an amplifier P, a triode VT1, a triode VT2, a triode VT3 and the like. The voltage buffer power supply has a great bandwidth, the dynamic response speed of the voltage buffer power supply can be improved, and the starting speed of an electrostatic dust collector is enabled to be higher. The voltage buffer power supply can improve the power factor, so that the efficiency of the voltage buffer power supply is improved. The voltage buffer power supply can also perform isolation on harmonic interference signals, so that a step-up transformer is avoidedfrom being polluted by harmonic waves, and the stability of the voltage buffer power supply is improved.

The invention provides a medium-high frequency power supply apparatus and an ozone generator. The medium-high frequency power supply apparatus comprises an alternating current input module, a phase shifting transformer and a power unit module, wherein the alternating current input module is used for leading in an alternating current; the primary side of the phase shifting transformer is electrically connected with the alternating current input module, and the secondary side of the phase shifting transformer has multiple output units; the power unit module comprises multiple power units, wherein the power units are used for converting the alternating current input into the power units into a direct current firstly and then reversing the direct current into a single-phase alternating currentwith preset voltage, current and frequency; each power unit is connected with one corresponding output unit on the secondary side separately; and the single-phase alternating current output ends of the respective power units are connected in series in an overlaid manner in sequence, so that the output voltage and frequency of the power unit module are equal to the sum of the output voltage and frequency of each power unit. By virtue of the medium-high frequency power supply apparatus and the ozone generator provided by the invention, harmonic pollution to a power grid can be prevented, and power factor is also improved.

The invention discloses an energy-saving elevator. The energy-saving elevator comprises a hoistway, a lift car, a linear motor, an energy-saving device and a frequency converter. The lift car is located in the hoistway and connected with the inner wall of the hoistway in a sliding mode. Each linear motor comprises a primary module and a secondary module, the primary modules are installed on the lift car, the secondary modules are installed on the hoistway, and the primary modules and the secondary modules are oppositely arranged. The energy-saving device comprises a storage battery and a converter, and the converter is connected to the storage battery. The frequency converter comprises a rectifier module, a direct-current module and an inverter module, the direct-current module is connected with the rectifier module and the inverter module, the inverter module is connected to the linear motor, and the converter is connected to the direct-current module. Energy generated under the power generation working condition of the elevator motor is stored in the energy-saving device through the frequency converter direct current module, energy waste is reduced, and the problem that current converted by potential energy is fed back to a power grid, and consequently harmonic pollution of the power grid is caused can be solved.

Provided total reactive power Q requested by system is supplied by n pieces of reactive compensation branch. A fixed capacitor is connected to a variable voltage source in one piece of compensation branch to supply 0-Q / n continuous controlled reactive power. Other n-1 pieces of compensation branch connect fixed capacitor to power source to supply fixed reactive powers. System reactive power is continuous controlled from 0-Q by continuous controlling reactive power in first piece of compensation branch and switching to other compensation branches. The capacity Qv of variable voltage source is only 1 / 4n of Q. Switching operation is implemented at time of zero current of all capacitors in n pieces of reactive compensation branch in order to avoid impulsion from electric network. Features are: low cost to realize reactive continuous control for electric network in high voltage, and prolonging service life of capacitor and switches.

The invention discloses an intelligent mixed type high-pressure dynamic reactive compensation device which comprises a compensation cabinet, a temperature controller and a heat dissipation fan. The temperature controller is used for controlling temperature inside the compensation cabinet. The compensation cabinet comprises a filter, a group of capacitors which are connected in parallel and a group of electric reactors which are connected in parallel. The electric reactors are adjustable electric reactors based on magnetic flux. A controller and a compensation control unit are further arranged inside the compensation cabinet. The controller is used for collecting three-phase high-voltage electricity. The compensation control unit comprises a trigger plate, a thyristor module and an insulated gate bipolar translator (IGBT) module. The compensation control unit receives a switching order of the controller, and is used for detecting of system parameters and compensation controlling of putting in and drawing out. The trigger plate adjusts the electric reactors in a double mode through the thyristor module and the IGBT module, a continuous stepless adjustable control mode is achieved, and adjusting range is wide.

The invention discloses a motor starting device and belongs to the technical field of motor starting equipment. The device provided by the invention comprises an inverter controller, an on-line digital detection system and a DSP (digital signal processor), wherein the inverter controller comprises a three-phase inverter bridge, compensation capacitor, reactors and the like; the three-phase inverter bridge is connected with a power receiving busbar of a motor through the three reactors (or transformers); the compensation capacitor is connected with the DC-side of the three-phase inverter bridge; and the on-line digital detection system, the DSP and the inverter controller form a closed-loop system. According to the invention, the starting device can rapidly track and compensate reactive current needed in the starting process of the motor in real time without producing harmonic current, can reduce voltage dip in the starting process of the motor and can shorten the start-up time of the motor.

The invention provides a charging circuit and a control method thereof. The charging circuit only comprises a group of BUCK charging circuit, the number of the devices is small, and the cost of the devices is relatively low. The voltage input of a single bus is still used, and the states of a first selection unit S1 and a first selection unit S2 are controlled by the input according to whether the voltage of the commercial power is in the positive half cycle or the negative half cycle at present, so that whether a positive bus or a negative bus is accessed is determined, the BUCK step-down ratio is low, the stress of a first switch device Q1 is small, the efficiency is high, the electrolysis capacity of the bus does not need to be large, and the cost of the device is lowered. The technical scheme solves the problems in the prior art that the imbalance of positive and negative buses is caused by load dissymmetry of positive and negative buses and input imbalance of PFC positive and negative semi-cycle power is caused, so that the harmonic pollution caused to the power grid is avoided.